The present invention is generally directed toward a process for preparing a copolymer. The process includes forming a first segment of the copolymer by using anionic polymerization techniques and then forming a second segment by using coordination catalysts.
Synthetically prepared conjugated diene polymers are commonly used in the rubber industry. These polymers are often prepared by using coordination-catalysts, which allow for control of the resulting microstructure. For example, polybutadiene having greater than 90 percent of its units in the 1,4-cis configuration can be produced with a coordination catalyst system that includes a nickel, cobalt, or titanium compound, an alkylating agent, and a halogen source. Polymers having this microstructure have a low glass transition temperature (Tg), which provides good low-temperature properties. Also, high 1,4-cis polymers have excellent wear resistance and mechanical properties such as reduced cut growth.
The tire industry has been challenged to design tires that have improved rolling resistance, which contributes to better fuel efficiency. Attempts thus far to address rolling resistance have included alternate tire designs and the use of rubber that has less hysteresis loss. In addressing the latter, the rubber industry has found that polymers that interact with tire fillers have demonstrated less hysteresis loss.
By using anionic polymerization techniques, polymers can be functionalized with filler-interactive groups both at initiation and termination. Unfortunately, however, anionic polymerization does not provide strict control over the polymer microstructure and therefore high 1,4-cis polymers are not obtained.
While many advantages can be attributed to anionically-polymerized polymers, and many others can be attributed to those polymers prepared with coordination catalysts, the combination of these advantages is highly desirable.
Unfortunately, however, the use of coordination catalysis has limited the ability to functionalize the resulting polymers. In the case of anionically-polymerized elastomers, the living nature of the resulting polymer allows for the addition of a modifying substituent by using simple chemical reactions such as nucleophilic substitution or addition reactions. In addition to end-functionalization, anionically-polymerized polymers can also be functionalized by using a functionalized initiator. But, since coordination catalysis operates by different chemical mechanisms that involve the interplay and interaction of several chemical constituents, and often also involves self-termination reactions, the chemistry and reaction conditions that are required to achieve funcitonalization are difficult to obtain.
Therefore, there is a need in the art to provide high-cis conjugated diene polymers, such as polybutadiene, that contain functional groups that will interact with or have an affinity toward carbon black and silica.
The present invention generally provides a process for forming a copolymer comprising the steps of (i) preparing a living polymer segment by using anionic polymerization techniques, (ii) modifying the living polymer by reacting it with an alkyl metal halide to form an organometallic polymeric intermediate, and (iii) preparing a second polymer segment from the organometallic polymeric intermediate by combining the intermediate, conjugated diene monomer, and a coordination catalyst that will polymerize the conjugated diene monomer.
The present invention also includes a copolymer prepared by the steps comprising (i) preparing a living polymer segment by using anionic polymerization techniques, (ii) modifying the living polymer by reacting it with an alkyl metal halide to form an organometallic polymeric intermediate, and (iii) preparing a second polymer segment from the organometallic polymeric intermediate by combining the intermediate, conjugated diene monomer, and a coordination catalyst that will polymerize the conjugated diene monomer.
The present invention further includes a tire comprising a copolymer prepared by (i) preparing a living polymer segment by using anionic polymerization techniques, (ii) modifying the living polymer by reacting it with an alkyl metal halide to form an organometallic polymeric intermediate, and (iii) preparing a second polymer segment from the organometallic polymeric intermediate by combining the intermediate, conjugated diene monomer, and a coordination catalyst that will polymerize the conjugated diene monomer.